The present invention relates to a chair on which a person can sit in a comfortable state regardless of his posture, that is, a working posture or an easy posture.
In general, in order that the person can sit on the chair in the comfortable state regardless of the working posture or the easy posture, it is desirable that when the back rest and the seat of the chair incline backward, by which the person shifts to the easy posture, the back rest inclines at an angle larger than the inclined angle of the seat and a bending angle of the knee is increased while the leg is inclining backward centering on the ankle without reducing the bending angle between the thigh and the leg (from the knee to the ankle), that is, the bending angle of the knee.
However, in a conventional chair of which seat 101 and back rest 102 are formed integrally as shown in FIG. 9 or the seat and the back rest separately incline backward in cooperation, with each other, a fulcrum 103 on which the seat inclines has been set under the center of the seat. In the chair which is designed as mentioned above, the seat inclines backward greatly, the leading edge thereof gradually rises as the seat inclines backward, by which feet of a person get out of bed, the bending angle of the knee is reduced and hence no comfortable feeling in an easy posture has been expected.
As a solution thereof, Japanese Patent Laid-Open Pub. No. 58-127617 discloses a chair which is designed such that the leading edge of the seat hardly rises, by which the rising of the feet is prevented.
However, the chair described in the above-mentioned Japanese Patent Laid Open Pub. No. 58-127617 is of the type in which even though a person rests against the back rest, by which the seat is drawn and moved backward and the leg inclines backward centering on the ankle as a fulcrum, the seat slightly inclines downward centering on the horizontal axis of the seat front part as a fulcrum and hence it has such a drawback that the thigh inclines downward to a state which is imperfect to increase the bending angle of the knee and hence it becomes impossible to sit in a comfortable easy posture.
In addition, in the above-mentioned chair, the fulcrum on which the seat inclines is set on the front part of the seat, so that the inclining angle of the seat is smaller than that of the back rest in comparison with a chair in which the seat inclining fulcrum is set on the center of the seat and hence it becomes impossible to reduce a load which is resolved in a forward and horizontal direction of the sitting face by the load of the body upper part of a sitter, which induces such a problem that the buttocks are pushed forward to slide along the sitting face in association with the inclining movement of the back rest and hence it is impossible to stably support the buttocks by the seat rear part.